Free-Diving

Samuel Gerson, MD

Undersea and Hyperbaric Medicine

Free-diving refers to various aquatic activities that share the practice of breath-hold diving. Breath-hold spear fishing Free-dive photography Competitive apnea Snorkeling Underwater hockey and rugby Mermaid show

Pool disciplines

Static Apnea Timed breath holding attempted with submersion in a pool.

Dynamic Apnea with (or without) fins. Horizontal underwater swimming in a pool for distance.

Depth disciplines

Constant Weight with (or without) fins. The athlete has to dive to the depth following a guide line but is not allowed to

actively use it during the dive. The ‘constant weight’ refers to the rule that you can not drop the weight during the dive.

Free Immersion The athlete uses the guideline & weight to actively pull him or herself down to depth

and back to the surface. It is known for its ease compared with the Constant Weight disciplines, while the athlete is not allowed to release weights.

Variable Weight The athlete uses a weighted sled for descent (release at bottom) and returns to the

surface by pulling themselves up along a line or swimming with their fins.

No Limits The athlete may use any means of breath-hold diving to depth and return to the

surface as long as a guideline is used to measure the distance. Most divers use a weighted sled to dive down and use an air-filled bag to return to the surface.

Official World Records

Static Apnea women: Natalia Molchanova (Russia, 2009), 8m23s men: Stephane Mifsud (France, 2009), 11m35s

Dynamic Apnea, without fins women: Natalia Molchanova (Russia, 2009), 160 meters men: Dave Mullins (United States, 2010), 218 meters

Dynamic Apnea women: Natalia Molchanova (Russia, 2010), 225 meters men: Goran Colak (Croatia, 2011), 273 meters

Official World Records

Constant Weight, without fins women: Natalia Molchanova (Russia, 2011), -66 metres men: William Trubridge (New Zealand, 2010), -101 metres

Constant Weight women: Natalia Molchanova (Russia, 2011), -101 metres men: Alexey Molchanov (Russia, 2012), -126 metres

Free Immersion women: Natalia Molchanova (Russia, 2011), -88 metres men: William Trubridge (New Zealand, 2011), -121 metres

Variable Weight women: Natalia Molchanova (Russia, 2012), -127 metres men: Herbert Nitsch (Austria), -142 metres

No limit women: Tanya Streeter (Cayman Islands, 2002), -160 metres men: Herbert Nitsch (Austria, 2007), -214 metres

Physiology

Chest compression (Boyle’s Law): 436 fsw dive, TLC of 9.6L compressed to

0.67L

If residual volume in this diver was 2.2L, how does this person avoid chest squeeze (how do you account for the ~1.5L difference)?

Answer: ~1.5L of blood is re-distributed from periphery to heart/lung.

Note: re-distribution of 700cc to lung has been shown at head-out-of water depths.

Duration depends on:

1.) Tolerance to hypercapnia & hypoxia

2.) Metabolic rate (cold H20 can increase this up to 277% in one report)

3.) C02 & 02 storage capacity

4.) Psychologic tolerance to unpleasant sensations of aphyxia

2 phases of breath-hold:

1.) Easy Going Phase

(diver relaxed, glottis closed,)

2.) Struggle Phase

a.) physiologic breaking point

(involuntary rhythmic inspiratory muscle contractions + closed

glottis)

b.) conventional breaking point

(involuntary rhythmic inspiratory muscle contractions + open

glottis)

Final phases of Ascent:

Decreased urge to breath: C02 levels which drive this urge are actually lower in low-pressure shallow H20.

Hypoxia of Ascent (Shallow H20 Blackout): Ie: If PA02 concentration at bottom (pressure of 9.1kPa) falls to 1.5%, Pa02 drops

to 68mmHg = still adequate for consciousness…

but at ascent when pressure drops to say only 4.0kPa an 02 concentration of only 1.5% yields a Pa02 of only 30mmHg = borderline for consciousness

Hyperventilation techniques prior to dive: delays hypercapnic respiratory drive long enough for hypoxia to cause

LOC and drowning.

Diving Response:

Result: Increased blood flow to ischemic prone heart and brain…decreased flow to ischemic resistant periphery.

Triggered by: Apnea

and/or

Cold water to face (especially V1 distribution)

Blunted response with age.

Diving Response:

Bradycardia slowest HR reported 5.6bpm yet cerebral perfusion maintained…C02 dilates cerebral arteries

Decrease Cardiac Output bradycardia

Increased Blood Pressure Peripheral sympathetic vasoconstriction outweighs bradycardia reports of fit expert divers with blood pressures of >280/200. Improves with dive duration.

Diving Response:

Splenic Contracture: Increased Hct by 9.5% (+/- 6%) after 115 dives to 20 fsw over 2.5 hrs Decreased spleen volume of 20% (+/-8%) Splenectomized divers = no change in Hct

Arrhythmias due to: Distention of heart (blood re-distribution) Increased vagal tone to heart